Unreliable and low-level constitutive transgene expression in plants is one of the major challenges in plant biotechnology applications for crop improvement and bio-pharming. Several molecular elements may play a role, but low-level expression of transgenes is primarily due to weak promoters. Currently, the choice of available promoters is limited and the majority of these promoters are based on conventional wild-type promoter elements of which the cauliflower mosaic virus 35S (CaMV 35S) is one of the most widely used promoters.
However, there is a need to drive transgene expression at levels higher than which is capable by the wild-type and even modified versions of CaMV 35S, especially for bio-pharming applications.